diff --git a/dec_arith_test.go b/dec_arith_test.go
new file mode 100644
index 0000000..9a3a597
--- /dev/null
+++ b/dec_arith_test.go
@@ -0,0 +1,59 @@
+package decimal
+
+import (
+	"math/rand"
+	"reflect"
+	"strconv"
+	"testing"
+	"time"
+)
+
+func TestAdd10VW(t *testing.T) {
+	td := []struct {
+		i dec
+		x Word
+		o dec
+		c Word
+		s int64
+	}{
+		{dec{_BD - 2, _BD - 1}, 2, dec{}, 1, 0},
+		{dec{_BD - 2, _BD - 1}, 1, dec{_BD - 1, _BD - 1}, 0, 0},
+		{dec{_BD - 2, _BD - 2}, 2, dec{0, _BD - 1}, 0, 0},
+	}
+	for i, d := range td {
+		t.Run(strconv.Itoa(i), func(t *testing.T) {
+			z := d.i
+			c := add10VW(z, z, d.x)
+			var s int64
+			z = z.norm()
+			if len(z) > 0 {
+				s = dnorm(z)
+			}
+			if !reflect.DeepEqual(z, d.o) || s != d.s || c != d.c {
+				t.Fatalf("addW failed: expected z = %v, s = %d, c = %d, got d = %v, s = %v, c = %v", d.o, d.s, d.c, z, s, c)
+			}
+
+		})
+	}
+}
+
+func TestDecDigits(t *testing.T) {
+	rand.Seed(time.Now().UnixNano())
+	for i := 0; i < 10000; i++ {
+		n := uint(rand.Uint64())
+		d := uint(0)
+		for m := n; m != 0; m /= 10 {
+			d++
+		}
+		if dd := decDigits(n); dd != d {
+			t.Fatalf("decDigits(%d) = %d, expected %d", n, dd, d)
+		}
+	}
+}
+
+func BenchmarkDecDigits(b *testing.B) {
+	rand.Seed(0xdeadbeefbadf00d)
+	for i := 0; i < b.N; i++ {
+		benchU = decDigits(uint(rand.Uint64()) % _BD)
+	}
+}
diff --git a/dec_conv.go b/dec_conv.go
index 423848e..323bd9b 100644
--- a/dec_conv.go
+++ b/dec_conv.go
@@ -98,7 +98,7 @@ func (z dec) scan(r io.ByteScanner, base int, fracOk bool) (res dec, b, count in
 				d1 = MaxBase + 1
 			}
 			if d1 >= b1 {
-				r.UnreadByte() // ch does not belong to number anymore
+				err = r.UnreadByte() // ch does not belong to number anymore
 				break
 			}
 			prev = '0'
diff --git a/dec_test.go b/dec_test.go
index cf88abe..5e8d30d 100644
--- a/dec_test.go
+++ b/dec_test.go
@@ -3,7 +3,6 @@ package decimal
 import (
 	"math/bits"
 	"math/rand"
-	"reflect"
 	"strconv"
 	"testing"
 	"time"
@@ -28,58 +27,6 @@ func TestDec_ntz(t *testing.T) {
 	}
 }
 
-func Test_mag(t *testing.T) {
-	rand.Seed(time.Now().UnixNano())
-	for i := 0; i < 10000; i++ {
-		n := uint(rand.Uint64())
-		d := uint(0)
-		for m := n; m != 0; m /= 10 {
-			d++
-		}
-		if dd := decDigits(n); dd != d {
-			t.Fatalf("mag(%d) = %d, expected %d", n, dd, d)
-		}
-	}
-}
-
-// TODO(db47h): remove this function
-func Test_dec_setInt(t *testing.T) {
-	// // TODO(db47h): next step
-	// b, _ := new(big.Int).SetString("12345678901234567890", 0)
-	// d, exp := dec{}.make(3).setInt(b)
-	// t.Log(d, exp)
-	// t.Log(string(dtoa(d, 10)))
-}
-
-func Test_add10VW(t *testing.T) {
-	td := []struct {
-		i dec
-		x Word
-		o dec
-		c Word
-		s int64
-	}{
-		{dec{_BD - 2, _BD - 1}, 2, dec{}, 1, 0},
-		{dec{_BD - 2, _BD - 1}, 1, dec{_BD - 1, _BD - 1}, 0, 0},
-		{dec{_BD - 2, _BD - 2}, 2, dec{0, _BD - 1}, 0, 0},
-	}
-	for i, d := range td {
-		t.Run(strconv.Itoa(i), func(t *testing.T) {
-			z := d.i
-			c := add10VW(z, z, d.x)
-			var s int64
-			z = z.norm()
-			if len(z) > 0 {
-				s = dnorm(z)
-			}
-			if !reflect.DeepEqual(z, d.o) || s != d.s || c != d.c {
-				t.Fatalf("addW failed: expected z = %v, s = %d, c = %d, got d = %v, s = %v, c = %v", d.o, d.s, d.c, z, s, c)
-			}
-
-		})
-	}
-}
-
 func TestDec_digit(t *testing.T) {
 	data := []struct {
 		d dec
@@ -107,27 +54,7 @@ var (
 	benchU uint
 )
 
-// func Benchmark_dnorm(b *testing.B) {
-// 	rand.Seed(0xdeadbeefbadf00d)
-// 	d := dec{}.make(10000)
-// 	for i := range d {
-// 		d[i] = Word(rand.Uint64()) % _BD
-// 	}
-// 	for i := 0; i < b.N; i++ {
-// 		d[0] = Word(rand.Uint64()) % _BD
-// 		d[len(d)-1] = Word(rand.Uint64()) % _BD
-// 		benchD, benchU = d.dnorm()
-// 	}
-// }
-
-func Benchmark_mag(b *testing.B) {
-	rand.Seed(0xdeadbeefbadf00d)
-	for i := 0; i < b.N; i++ {
-		benchU = decDigits(uint(rand.Uint64()) % _BD)
-	}
-}
-
-func Benchmark_dec_Digits(b *testing.B) {
+func BenchmarkDec_Digits(b *testing.B) {
 	rand.Seed(0xdeadbeefbadf00d)
 	d := dec{}.make(10000)
 	for i := range d {
diff --git a/decimal_test.go b/decimal_test.go
index 361718a..53e0377 100644
--- a/decimal_test.go
+++ b/decimal_test.go
@@ -91,3 +91,16 @@ func TestDecimal_SetString(t *testing.T) {
 	// 	})
 	// }
 }
+
+func BenchmarkDnorm(b *testing.B) {
+	rand.Seed(0xdeadbeefbadf00d)
+	d := dec{}.make(1000)
+	for i := range d {
+		d[i] = Word(rand.Uint64()) % _BD
+	}
+	for i := 0; i < b.N; i++ {
+		d[0] = Word(rand.Uint64()) % _BD
+		d[len(d)-1] = Word(rand.Uint64()) % _BD
+		benchU = uint(dnorm(d))
+	}
+}